1. Field of the Invention
The present invention concerns a motor vehicle starter.
The invention concerns more particularly a motor vehicle starter of the type having a casing in which there is arranged an electric motor whose output shaft rotates a coaxial starter head with the interposing of an epicyclic gearbox comprising a gear wheel made of rigid material, with internal teeth, which is housed at least partially in a cavity in the casing in which it is immobilised with respect to rotation by means by cooperation of shapes and which has an internally toothed cylindrical annular skirt closed at its front axial end by a radially oriented transverse wall with a hole at its centre for an output shaft of the gearbox to pass.
2. Description of Related Art
The compression times of the thermal engine, during the driving phase, cause variations in load and the taking up of angular play in the different gears. The result is vibrations and shocks harmful to the service life of the starter. This phenomenon is accompanied by an emission of sound sufficiently intense to be perceived unpleasantly by the user.
According to a known design, in order to reduce the high mechanical overloads transmitted to the rotating components of the starter, which result from the abrupt variations in speed arising during the starting period because of the abrupt slowing of the thermal engine which can occur following the first explosions which are too far advanced with respect to the passage through top dead centre of the pistons, it has been proposed to associate, with an epicyclic gearbox, one or more dampers consisting of blocks of rubber which stop the ring gear of the gear train rotation-wise.
This solution is however bulky, uses additional components and causes a high additional cost whilst complicating the operations of assembling the components of the gearbox and/or starter.
The object of the invention is to propose a novel design of starter of the type mentioned above which remedies the drawbacks which have just been mentioned.
For this purpose, the invention proposes a starter, characterised in that the ring gear has pins moulded from a flexible material, notably elastomer, which are interposed between the ring gear and complementary portions of the cavity of the casing in order to immobilise the ring gear rotation-wise with respect to the casing and provide a torsion damping function between these two components.
According to other characteristics of the invention:
the cylindrical external surface of the skirt of the ring gear is provided with a vibration-isolating peripheral layer which is moulded from the said flexible material and which is interposed between the skirt and the complementary portions of the cavity forming a housing for the skirt of the ring gear;
the damping pins and the vibration-isolating peripheral layer are produced by overmoulding on the ring gear;
the ring made of rigid material on the one hand and the damping pins and isolating peripheral layer made of flexible material on the other hand are produced simultaneously according to the technique of moulding two materials, rigid and flexible respectively;
the damping pins extend axially forwards from the external face of the transverse wall of the ring gear and cooperate through their axially oriented opposite lateral faces with portions of facing surfaces, each pair of which delimits laterally a complementary axial groove formed in the cavity of the casing;
the ring gear has a series of connecting arms which extend axially, from the external face of its transverse wall, inside the damping pins;
the transverse wall of the ring gear has a series of emerging axial holes, through each of which there extends a flexible material for moulding a damping pin to constitute a foot for anchoring the corresponding pin on the ring gear;
the damping pins are distributed angularly in a regular manner around the axis of the ring gear;
the central hole in the ring gear delimits a bearing for the rotational guidance of the output shaft of the gearbox, and the internal surface of the bearing is provided with a vibration-isolating layer which is moulded from the said flexible material and which is interposed between the internal surface of the bearing and a bearing shell for guiding the output shaft in rotation;
the peripheral isolating layer has a rib for the angular location of the ring gear in the cavity of the casing.